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Essential theory and proven techniques for acoustic echo and noise suppression
Today’s voice communication systems, with their increasing demand for user comfort, necessitate a growing focus on acoustic noise suppression and echo reduction. Drawing on the results of a twenty-year career with the Signal Theory Group at Darmstadt University of Technology, Darmstadt, Germany, Acoustic Echo and Noise Control: A Practical Approach addresses proven methods for suppressing acoustic echoes and noise in various sound systems, from hands-free telephones to video conferencing systems, hearing aids, and speech recognition systems.
With emphasis on single-channel systems, the authors, both recognized experts in the field, deliver a combination of theoretical research and practical solutions to acoustical problems across a broad range of industries. In addition to presenting a detailed description of practical methods for controlling acoustic echoes and noise, they also develop a theory for optimal control parameters and present practical estimation and approximation methods.
Some of the topics covered include:
- Basic algorithms for filtering, linear prediction, and adaptation of filter coefficients
- Application of these algorithms to acoustic echo cancellation and residual echo and noise suppression
- Estimation of nonmeasurable quantities necessary to control algorithms
- Devising control structures based on these quantities
Requiring only a basic knowledge of linear systems theory and digital signal processing, this text offers an ideal resource for students, researchers, and systems engineers seeking to familiarize themselves with the latest developments and practical applications in this fascinating field.
List of Figures.
List of Tables.
Preface.
Acknowledgments.
Abbreviations and Acronyms.
Part I: Basics.
1 Introduction.
1.1 Some History.
1.2 Overview of the Book.
2 Acoustic Echo and Noise Control Systems.
2.1 Notation.
2.2 Applications.
3 Fundamentals.
3.1 Signals.
3.2 Acoustic Echoes.
3.3 Standards.
Part II: Algorithms.
4 Error Criteria and Cost Functions.
4.1 Error Criteria for Adaptive Filters.
4.2 Error Criteria for Filter Design.
4.3 Error Criteria for Speech Processing and Control Purposes.
5 Wiener Filter.
5.1 Time-Domain Solution.
5.2 Frequency-Domain Solution.
6 Linear Prediction.
6.1 Normal Equations.
6.2 Levinson{Durbin Recursion.
7 Algorithms for Adaptive Filters.
7.1 The Normalized Least Mean Square Algorithm.
7.2 The Affine Projection Algorithm.
7.3 The Recursive Least Squares Algorithm.
7.4 The Kalman Algorithm.
Part III: Acoustic Echo and Noise Control.
8 Traditional Methods for Stabilization of Electroacoustic Loops.
8.1 Adaptive Line Enhancement.
8.2 Frequency Shift.
8.3 Controlled Attenuation.
9 Echo Cancellation.
9.1 Processing Structures.
9.2 Stereophonic and Multichannel Echo Cancellation.
10 Residual Echo and Noise Suppression.
10.1 Basics.
10.2 Suppression of Residual Echoes.
10.3 Suppression of Background Noise.
10.4 Combining Background Noise and Residual Echo Suppression.
11 Beamforming.
11.1 Basics.
11.2 Characteristics of Microphone Arrays.
11.3 Fixed Beamforming.
11.4 Adaptive Beamforming.
Part IV: Control and Implementation Issues.
12 System Control\—Basic Aspects.
12.1 Convergence versus Divergence Speed.
12.2 System Levels for Control Design.
13 Control of Echo Cancellation Systems.
13.1 Pseudooptimal Control Parameters for the NLMS Algorithm.
13.2 Pseudooptimal Control Parameters for the Affine Projection Algorithm.
13.3 Summary of Pseudooptimal Control Parameters.
13.4 Detection and Estimation Methods.
13.5 Detector Overview and Combined Control Methods.
14 Control of Noise and Echo Suppression Systems.
14.1 Estimation of Spectral Power Density of Background Noise.
14.2 Musical Noise.
14.3 Control of Filter Characteristics.
15 Control for Beamforming.
15.1 Practical Problems.
15.2 Stepsize Control.
16 Implementation Issues.
16.1 Quantization Errors.
16.2 Number Representation Errors.
16.3 Arithmetical Errors.
16.4 Fixed Point versus Floating Point.
16.5 Quantization of Filter Taps.
Part V: Outlook and Appendixes.
17 Outlook.
Appendix A: Subband Impulse Responses.
A.1 Consequences for Subband Echo Cancellation.
A.2 Transformation.
A.3 Concluding Remarks.
Appendix B: Filterbank Design.
B.1 Conditions for Approximately Perfect Reconstruction.
B.2 Filter Design Using a Product Approach.
B.3 Design of Prototype Lowpass Filters.
B.4 Analysis of Prototype Filters and the Filterbank System.
References.
Index.
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